In modern cities, dogs must be controlled when outside the owner's property and trained to acceptable behavior in any location. Dogs must also be exercised when not allowed to run free, most generally by being taken on walks. Most dogs have collars for attachment to a leash. A rambunctious or energetic dog will pull on a leash, which is unpleasant for the human and can cause dangerous falls. Many collars are available for controlling a dog on walks. The Halti® halter gives some steering power by a strap over the dog's muzzle which, when pulled, turns the dog's head. The Gentle Leader® head collar gives more sophisticated control by allowing simultaneous pressure on the muzzle and the back of the head of the dog, which stimulates natural behavioral signals in the dog.
Harnesses for dogs have been well known for many years and are useful for controlling a dog. In its simplest form, a harness is constructed of one or two straps around the torso at the thorax or belly, connected at to a strap around the chest. The torso strap can be configured to be placed high on the chest and rising to the top of the back. A leash is usually attached at the back. There are several problems with a back attachment. Pressure may be put on sensitive areas of the body, particularly the axial plexus, when the leash is pulled or if the torso strap is too high on the chest. The most limiting problem is that pulling on the leash triggers an opposition reflex. Dogs have evolved to have a reflex causing them to move toward a pressure on their body. A most sensitive point to trigger the opposition reflex is the center of the chest. Therefore, a dog being walked with a harness attached at the back of the neck or shoulders will tend to pull against a leash, causing problems for the handler, including straining the handler's back or injuring the arm due to the dog's strong pull on the leash. A sudden lunge by the dog can result in the handler's falling, especially on slick or icy paths.